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Biogas that used to be flared now flows from the digestersat the Willingboro treatmentplant through a gas treatment system before powering a microturbine. Combined with a photovoltaic system, the plant will get nearly 60 percent of its electricity fr

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An initial estimate of $12 million didn’t scare away the Willingboro (N.J.) Municipal Utilities Authority from adding substantial renewable energy resources. It helped when project costs came in much lower than first thought.

Then funds from the American Reinvestment and Recovery Act (federal stimulus) and New Jersey renewable energy rebates made the picture that much brighter.

“We have a positive cash flow in the first year,” says Joe Bateman, executive director. The work included solar photovoltaic installations at the Willingboro Pollution Control Facility (879,500 kWh/yr) and the city’s water treatment plant (271,000 kWh/yr). The total cost was about $8 million: $2.5 million at the water treatment plant and $5.6 at the wastewater plant. ARRA funds paid 45 percent, and state rebates will cover the rest.

Bateman had no reservations about adding such a large solar facility. “I had no hesitation,” he says. “The payback would have been much longer, but being awarded the state and federal funding made it a no-brainer.”

Positive reactions

The wastewater plant also added a Capstone C65 microturbine and gas cleanup unit to generate 550,000 kWh per year from digester gas. “It was initially a cost-control, business-driven decision,” adds Bateman, “but we also looked at what we would contribute to our community, the region, and the state from a green perspective, and the positive public relations.”

He says the public appreciates both the efforts to be a better steward of the environment and to save customers money. All told, the renewable energy work will reduce the authority’s energy costs by about 25 percent — $300,000 per year — saving every customer just over $19 annually. “We can pass on the savings to customers, or at least mitigate future rate increases,” Bateman says. “Energy costs are our second-largest cost of operation.”

Using the sun will also decrease annual emissions of carbon dioxide by nearly 1.7 million pounds, sulfur dioxide by 6,500 pounds, and nitrogen dioxide by 2,500 pounds, in addition to a significant reduction in mercury, according to Bateman.

Energy credits

The Willingboro Pollution Control Facility is a 5.5 mgd two-stage trickling filter plant serving 65,000 people in and around the city, just northeast of Philadelphia. The solar installation went online in October 2010; about a month after the water treatment plant’s solar panels went into operation.

Along with the positive cash flow in the first year, the city’s utility department will be able to sell renewable energy credits through PJM Interconnection, the regional power manager. The credits will earn the utility about $580,000 a year.

There are 3,300 Sharp Electronics NU-U230 photovoltaic panels mounted in a fixed array on five acres of plant property, and another 2,000 at the water treatment plant. The least expensive type of solar installation, a fixed array does not move with the sun, limiting its total output.

Bateman says project engineers from Alaimo Group and general contractor APS Contracting considered a tracking system. “It would have been somewhat better, but the calculations showed that the increase in maintenance and capital costs over the life of the project would be more than we would save,” he recalls. Tracking systems are generally better in areas that get high levels of usable sunshine year-round.

No trade-off

Such a trade-off decision wasn’t necessary with the microturbine project from Unison with an Applied Filter Technology siloxane removal system. That project became fully operational in spring 2011. “We just had to tap into the gas with a new valve,” Bateman says. “Instead of flaring it off, we just redirected the gas to the microturbine.”

Together, the solar system and microturbine will generate about 58 percent of the wastewater plant’s electrical needs. The next step is to see if increased biogas production will pay off. “There is sufficient gas production in our two-stage digester,” says Bateman. “We are looking at better mixing in the digester and perhaps the addition of some FOG from our local restaurants to increase our gas production and keep that waste out of the landfills.”